1. Field of the Invention
This invention relates to preparation of and water oxidation by functionally substituted bidentate ligand oxo-bridged ruthenium dimers. The dimer catalysts have high activity to catalyze oxygen evolution close to equilibrium conditions and provide good catalyst stability.
2. Description of the Prior Art
Catalysts for oxidation of water to molecular oxygen are critical in obtaining an energy efficient water splitting process. Various ruthenium complexes have been investigated in recent years as water oxidation catalysts.
Cis-trans photoisomerism and ClO.sub.4.sup.- oxidation of Ru(bpy).sub.2 (OH.sub.2).sub.2.sup.+ is taught by Durham, B., Wilson, S. R., Hodgson, D. J., Meyer, T. J., J. Am. Chem. Soc. 1980, 102, pg. 600. A number of mononuclear bis(diimine) complexes of ruthenium (II) were shown to have no activity toward the oxidation of water while the dinuclear (bpy).sub.2 (H.sub.2 O)RuORu(H.sub.2 O)(bpy).sub.2.sup.4+ was confirmed to be a catalyst for generation of O.sub.2 from water. Collin, J. P.; Sauvage, J. P., Inorg. Chem. 1986, 25, pg. 135. Use of a catalyst of oxo-bridged dimeric system of ruthenium (III), [(bpy).sub.2 (H.sub.2 O)RuORu(H.sub.2 O)(bpy).sub.2 ].sup.4+ is reported upon oxidation by four equivalents to provide rapid oxidation of water. Gersten, S. W., G. J. Samuels, T. J. Meyer, J. Am. Chem. Soc. 1982, 104, pg, 4029. Photochemistry of ruthenium complexes for water oxidation has been investigated using [Ru(2,2'-bipyridine).sub.3 ].sup.3+ with molecular oxygen evolution resulting from formation of binuclear oxo complexes which act as catalysts in the presence of [Ru(bpy).sub.3 ].sup.3+ for the oxidation of water to molecular oxygen. Lay, P. S. W. H. F. Sasse, Inorg. Chem. 1985, 24, pg. 4707. Photochemical catalytic oxidation of water in homogeneous media and in colloidal SiO.sub.2 suspensions by the dimer [(bpy).sub.2 (H.sub.2 O)RuORu(H.sub.2 O)(bpy).sub.2 ].sup.4+ is shown by Honda, K., A. J. Frank, J. Chem. Soc., Chem. Commun. 1984, pg. 1635. The redox properties of the water oxidation catalyst [(bpy).sub.2 (H.sub.2 O)RuORu(H.sub.2 O)(bpy).sub.2 ].sup.4+ are taught by Gilbert, J. A., D. S. Eggleston, W. R. Murphy, D. A. Geselowitz, S. W. Gersten, D. J. Hodgson, T. J. Meyer, J. Am. Chem. Soc. 1985, 107, pg. 3855.
Oxygen generation under visible light illumination of highly acidic aqueous solutions of tris (2,2-bipryidine-4,4'dicarboxylic acid) ruthenium(II) containing S.sub.2 O.sub.8.sup.2- as an electron acceptor in the absence of a heterogeneous redox catalyst is taught by Desilvestro, J., D. Duonghong, M. Kleiujn, M. Gratzel, Chimia 1985, 39, 4, pg. 102.
A water oxidation catalyst generated in situ from cis-RuL.sub.2 (OH.sub.2).sub.2 where L=2,2'-bipyridine-5,5'-dicarboxylic acid is taught by A Molecular Water-Oxidation Catalyst, Frank, A. J., M. Gratzel, J. K. Hurst, F. Pern, Abstracts of Papers, 193rd ACS National Meeting, Am. Chem. Soc., Denver, Colo., Apr. 5-10, 1987. In this paper there was no disclosure of the dimeric form of the catalyst, electrochemical method for preparation of the catalyst, nor any disclosure of conditions required for water oxidation using the catalyst.